Aqueous dispersion with finely divided, non ionic plastics

ABSTRACT

An aqueous dispersion based on an acid-protonized reaction product from 
     (a) Mannich bases free from epoxide groups, from 
     (a 1 ) condensed phenols free from ether groups with at least two aromatic rings and with at least two phenolic hydroxyl groups and/or 
     (a 2 ) condensed phenols, containing ether groups, with at least two aromatic rings and at least one phenolic hydroxyl group 
     (a 3 ) secondary amines with at least one hydroxyalkyl group, possible in a mixture with 
     (a 4 ) secondary dialkylamines or dialkoxyalkylamines without free hydroxyl groups, 
     (a 5 ) formaldehyde or compounds splitting off formaldehyde, with 
     (b) epoxide resins, aliphatic hydroxyl groups from (a) and/or (b) being converted at least in part into urethane groups possibly by reaction with partly blocked isocyanates, 
     containing furthermore fine-particulate non-ionic plastics in dispersed form. The dispersion and/or the fine-particulate plastics furthermore may contain pigments and/or fillers. The dispersion is suitable as an electro-dip means for coating on electrically conducting substrates acting as the cathodes in an electro-dip enameling process.

The invention relates to an aqueous dispersion composed of finelydivided plastics. It is suitable as an electrocoating bath for theproduction of coatings on electrically conducting substrates which areconnected as the cathode in an electrocoating lacquering process.

Aqueous dispersions of plastics which produce film formation under theinfluence of heat, or produce crosslinking, are known. When used by theconventional methods of application of brushing, dipping and spraying,they produce fault-free, serviceable coatings.

The object of the present invention was to enable aqueous dispersionscomposed of finely divided plastics also to be used in an electrocoatinglacquering process as an electrocoating bath, the substrate to be coatedbeing connected as the cathode while direct current is being passed andthe coating bath having a pH value between 7 and 9. The conventionalcationic systems, by means of which it is possible to coat theelectrically conducting substrates, connected as the cathode, in anelectrocoating lacquering process by applying direct current oralternating current, have a bath pH value considerably below 7. A low pHvalue results from neutralizing the cationic resin with acid. Theconsequence of a pH value in the acid range is increased corrosion ofthe installation in the liquid and gaseous phases.

The extent of the dissociation of the acid used for dispersing and forneutralizing varies according to the pH value of the electrocoatingbath. The undissociated fraction is larger at a low pH value of the bathand, depending on the vapor pressure of the acid and on the temperatureof the bath, this fraction is responsible, to a varying extent, for thecorrosive attack on the material of the installation in the liquid andgaseous phases.

The object has been achieved, surprisingly, by means of an aqueousdispersion composed of finely divided plastics, wherein finely divided,nonionic plastics are dispersed in an aqueous solution and/or aqueousdispersion, having a pH value between 7 and 9, of a product, protonatedwith acids, from the reaction of (a) Mannich bases which are free fromepoxide groups and are formed from (a₁) condensed phenols which are freefrom ether groups and contain at least two aromatic rings and at leasttwo phenolic hydroxyl groups, and/or (a₂) condensed phenols whichcontain ether groups and contain at least two aromatic rings and atleast one phenolic hydroxyl group, (a₃) secondary amines having at leastone hydroxyalkyl group, if appropriate mixed with (a₄) secondarydialkylamines or dialkoxyalkylamines which do not contain free hydroxylgroups, and (a₅) formaldehyde or compounds which split off formaldehyde,with (b) epoxide resins, aliphatic hydroxyl groups originating from (a)and/or (b) being optionally converted, at least partially, into urethanegroups by reaction with partially blocked isocyanates.

Aqueous dispersions which are preferentially suitable are thosecontaining pigments and/or fillers and/or water-miscible organicsolvents which do not either incipiently dissolve or incipiently swellthe finely divided plastics.

In a particularly preferred embodiment of the invention, the finelydivided, nonionic plastics can already contain pigments and/or fillers.

The invention also relates to the use of the aqueous dispersionsaccording to the invention for the production of coatings on the surfaceof electrically conducting substrates, connected as the cathode, bycathodic deposition from a coating bath in a cathodic electrocoatinglacquering process and subsequently stoving the coating.

Both the finely divided, nonionic plastics and the reaction productformed from Mannich bases and epoxide resins can be cathodicallydeposited evenly at a pH value above 7 from the aqueous dispersionsaccording to the invention, and they produce, after a brief coatingtime, coatings of up to 150 μm which have, after stoving, outstandingmechanical properties, such as high hardness and scratch resistancetogether with good elasticity and firm adhesion to the substrate.

After stoving at temperatures of up to 200° C., for a stoving time ofabout 15 minutes, the coatings have exceptionally good corrosionresistance. Values up to 1,000 hours are achieved in the salt spray testas specified in German Industrial Standard DIN 50,021. Theelectrochemical efficiency is high; the electrochemical equivalent is 5to 20 coulombs (C) per gram of coating deposited.

It has also been found that the surface of the stoved coating is sosmooth that a single top layer of lacquer is sufficient to achieve alacquer coating with a good appearance.

The reaction product formed from Mannich bases which are free fromepoxide groups, and epoxide resins is present in a protonated form inthe aqueous dispersion according to the invention and acts as a carrierresin for the finely divided, nonionic plastics. It will be designated"carrier resin" in the test which follows. The carrier resin isprotonated by means of suitable inorganic and/or organic acids,preferably water-soluble carboxylic acids, and, in the protonated form,it is soluble or dispersible in water or can be mixed and diluted withwater. The pH value of the aqueous solution or aqueous dispersion isadjusted to a value between 7 and not more than 9.

Suitable acids are virtually all known inorganic and organic acids, suchas, for example, hydrochloric acid, sulfuric acid, phosphoric acid,carbonic acid, p-toluenesulfonic acid, acetic acid, propionic acid,formic acid, citric acid, lactic acid, malic acid, fumaric acid, maleicacid and phthalic acid and also the half-esters of fumaric acid, maleicacid and phthalic acid with monohydric or polyhydric aliphatic alcohols,such as methanol, ethanol, propanol or ethylene glycol. The best resultsare obtained using acetic acid, lactic acid and formic acid, which aretherefore suggested as preferentially suitable protonating agents. Thecarrier resin is preferably used in coating agents for the cathodicelectrocoating lacquering of electrically conducting substrates, forexample metal parts made of aluminium, brass, copper, iron, steel andiron alloys containing other metals, which can be given a chemicalpre-treatment, for example can be phosphatized.

The preparation of the protonated reaction product formed from Mannichbases which are free from epoxide groups, and epoxide resins is knownfrom German Offenlegungsschrift No. 2,751,499 and is not claimed in thistext.

In order to characterize the reaction product unambiguously, however,the following should be stated in regard to the individual components:

The Mannich bases (a) containing no epoxide groups are prepared from(a₁) condensed phenols which are free from ether groups and contain atleast two aromatic rings and at least two phenolic hydroxyl groups,and/or (a₂) condensed phenols which contain ether groups and contain atleast two aromatic rings and at least one phenolic hydroxyl group, (a₃)secondary amines having at least one hydroxyalkyl group, if appropriatemixed with (a₄) secondary dialkylamines or dialkoxyalkylamines which donot contain free hydroxyl groups, and (a₅) formaldehyde or compoundswhich split off formaldehyde.

Condensed phenols which are free from ether groups and contain at leasttwo aromatic rings and at least two phenolic hydroxyl groups (a₁) whichare particularly suitable are condensed phenols of the general formula##STR1## wherein the hydroxyl groups are in the ortho-position orpara-position in relation to X and X is a straight-chain or branched,divalent aliphatic radical having 1 to 3 carbon atoms, or SO₂, SO or##STR2## (in which R=alkyl radical having 1 to 6 C atoms); bisphenol Ais particularly suitable. Low-molecular reaction products formed fromphenols and formaldehyde, so-called novolacs, can also be employed.

If appropriate, it is possible to use, as a mixture with the condensedphenols (a₁) or instead of the latter, further condensed phenols (a₂)which contain at least one phenolic hydroxyl group and, in addition,also one or more ether groups in the molecule. These products have thegeneral formula

    HO--B--[O--E--O].sub.n --H

and/or

    HO--B--[O--E--O].sub.n --P

wherein B represents the radical ##STR3## and X has the meaningindicated above, E represents a radical which contains hydroxyl groupsand has been obtained by adding an epoxide compound onto a phenolichydroxyl group, P represents a phenyl or alkylphenyl radical and nrepresents an integer from 1 to 3, and wherein epoxide resins, such as,for example, diglycidyl ethers of bisphenol A, pentaerythritol,glycerol, trimethylolpropane, glycol, glycol ethers and otherpolyhydric, preferably dihydric to tetrahydric alcohols, are preferablyemployed as the epoxide compounds (for E).

If the condensed phenols (a₂) are to be used on their own, it isappropriate to select those based on triglycidyl or tetraglycidylethers.

Other suitable compounds containing epoxide groups arenitrogen-containing diepoxides, such as are described in U.S. Pat. No.3,365,471, epoxide resins obtained from 1,1-methylene-bis-(5-substitutedhydantoin) in accordance with U.S. Pat. No. 3,391,097, diepoxidesobtained from bisimides in accordance with U.S. Pat. No. 3,450,711,epoxylated aminomethyldiphenyl oxides according to U.S. Pat. No.3,312,664, heterocyclic N,N'-diglycidyl compounds according to U.S. Pat.No. 3,503,979, aminoepoxy phosphates according to British PatentSpecification No. 1,172,916 or 1,3,5-triglycidyl isocyanurates.

Components (a₂) which are particularly preferred are the products formedfrom the reaction of diglycidyl ethers of bisphenol A or of polyhydricaliphatic alcohols, such as pentaerythritol, trimethylolpropane andglycerol, with bisphenol A and, if appropriate, phenol, which containphenol groups and are virtually free from epoxide groups. Such productsgenerally have molecular weights from 650 to 1,300 and epoxide valuesfrom 0.004 to 0.01 and can be prepared, for example, at temperaturesbetween 160° and 180° C., or at correspondingly lower temperatures inthe presence of catalysts for the reaction.

The condensed phenols (a₂) contain aliphatically linked hydroxyl groups.Some of these are formed from the epoxide groups of the epoxide resins(E) in the reaction of the latter with the bisphenols (B) or with thephenols (P). However, hydroxyl groups can also already be present in theepoxide resins themselves, if the latter have been prepared by reactingalcohols of a functionality higher than dihydric (for examplepentaerythritol, trimethylolpropane or glycerol) with 2 moles ofepichlorohydrin.

In the case which is in itself preferred, in which mixtures of thecomponents (a₁) and (a₂) are employed, the ratio by weight of the twocomponents is between 1:0.1 and 1:5.

Examples of suitable secondary amines (a₃) which contain at least onehydroxyalkyl group, are alkylethanolamines or alkylisopropanolamineshaving 1 to 6 carbon atoms in the alkyl group. Dialkanolamines ofalcohols having 2 to 6 carbon atoms, in particular diethanolamine, andalso mixtures of these dialkanolamines with alkylalkanolamines arepreferred, however.

The seconary amines (a₃) which are incorporated in the Mannich bases (a)as dialkanolaminomethyl groups and alkylalkanolaminomethyl groups, areof considerable importance for the degree of dispersibility of thebinders in the desired pH range of 6.0 to 10.2 and for the crosslinkingof the system.

Suitable secondary dialkylamines or dialkoxyalkylamines (a₄) which areemployed conjointly with the amines (a₃) containing hydroxyalkyl groupsfor the preparation of the Mannich bases, are those of the generalformula ##STR4## in which R₁ and R₂ are identical or different andrepresent a straight-chain or branched aliphatic radical which has 2 to10 carbon atoms and can contain alkoxy groups. Examples of suitablesecondary amines of this type are di-n-butylamine, di-n-propylamine,diisopropylamine, di-n-pentylamine, di-n-hexylamine, di-n-octylamine,di-2-ethylhexylamine and di-2-alkoxyethylamines, such as, for example,di-2-methoxyethylamine, di-2-ethoxyethylamine or di-2-butoxyethylamine,and also secondary amines in which R₁ and R₂ are linked to form a ring,such as, for example, morpholine or piperidine.

Di-n-butylamine, di-2-ethylhexylamine and di-n-hexylamine arepreferentially suitable. The mode of action of these secondary amines(a₄) consists chiefly in influencing the stability properties of thebinders, in addition they contribute to the levelling and to the"internal plasticization" of the lacquer films produced from thebinders. They also make a certain contribution to the crosslinking.

As a result of their mode of preparation, the secondary amines can alsocontain, inter alia, proportions of corresponding primary amines, butthe proportion of these should not exceed 20 percent by weight of thesecondary amines. The ratio by weight of the components (a₃) and (a₄)can be between 1:10 and 1:0.1, preferably between 1:2 and 2:1.

Aqueous or alcoholic, such as, for example, butanolic, solutions offormaldehyde or paraformaldehyde or mixtures thereof are used asformaldehyde or compounds which provide formaldehyde (a₅).

The Mannich bases (a) are prepared by the customary methods indicated inthe literature (compare, for example, Houben-Weyl, Methoden derorganischen Chemie ("Methods of Organic Chemistry"), Volume XI/1, page731 (1957)), preferably by carrying out the reaction at temperaturesbetween 20° and 80° C. The proportions of the starting materialsemployed depend on the particular properties desired, the molar ratio ofthe components (a₁) and (a₂) to the components (a₃) and (a₄) beingpreferably 1:0.75 to 1:3. In general, however, about one mole ofsecondary amine is employed for each phenolic hydroxyl group. Thequantity of (a₅) is at least one mole, relative to one mole of secondaryamine.

The Mannich bases (a) which are free from epoxide groups are reacted ina quantity of 50 to 90, preferably 60 to 80, percent by weight, with 5to 50, preferably 10 to 30, percent by weight of epoxideresin--component (b). The reaction of the component (a) with thecomponent (b) is generally carried out at temperatures from 20° to 100°C., preferably 60° to 80° C., if appropriate in the presence of organicsolvents, such as, for example, alcohols, glycol ethers and ketones. Thereaction product obtained is substantially free from epoxide groups.

The reaction of (a) with (b) to give the reaction product is describedin patent applications German Published Specification No. 2,419,179,German Published Specification No. 2,320,301, German PublishedSpecification No. 2,357,075, German Published Specification No.2,541,801 and German Published Specification No. 2,554,080.

Suitable epoxide resins (component b) are preferably polyepoxidecompounds having 2 to 3 epoxide groups in the molecule, such as, forexample, products from the reaction of polyhydric phenols, particularlythose of the formula ##STR5## mentioned under (a₁), withepichlorohydrin; but also the abovementioned products from the reactionof polyhydric alcohols, such as, for example, pentaerythritol,trimethylolpropane or glycerol, with epichlorohydrin; also products,containing epoxide groups, from the reaction of epoxide resins withsecondary amines or glycol ethers containing hydroxyl groups; and alsoepoxide resins which contain incorporated hetero-atoms, such as sulfur.

In general, the epoxide resins (b) also contain aliphatically linkedhydroxyl groups, particularly if a condensation reaction to formhigher-molecular products has taken place in the reaction of thepolyhydric alcohol.

Some of the aliphatically linked hydroxyl groups from (a) or (b) can, ifappropriate, be converted into urethane groups. The reaction of thehydroxyl groups with the partially blocked polyisocyanates can becarried out at any desired stage of the preparation of the binders; itis preferable to react the epoxide resins. This can be effected not onlywith the epoxide resins constituting the component (b) but also with theepoxide resins (E) which are employed for the preparation of thecomponent (a₂). It is also possible to react the finished component (a₂)directly with the partially blocked polyisocyanate. If epoxide resinsbased on polyhydric aliphatic alcohols, for example pentaerythritol, areused, the attack of the isocyanate takes place preferentially at thefree primary alcohol group; there is only a secondary reaction at thesecondary alcohol group which has been formed from the epoxide ring.Under the conditions selected, phenolic hydroxyl groups remain in themain unchanged. Any amino or imino groups which may be present can alsoreact with the partially blocked polyisocyanates, which can be desirablein some cases.

The reaction is usually carried out at temperatures from 50° to 120°,preferably from 70° to 100° C., and conventional catalysts for theformation of polyurethanes, such as, for example, dibutyltin dilaurate,can be present. The reaction is carried out in the absence of polarsolvents; it is preferable to carry out the reaction in the melt, butinert diluents can also be present.

Aromatic diisocyanates, such as toluylene diisocyanates or xylylenediisocyanates or dimers and trimers thereof, are particularly suitableas partially blocked polyisocyanates. However, it is also possible touse aliphatic diisocyanates, such as hexamethylene diisocyanate, andalso prepolymers which are prepared by reacting polyols or polyetherpolyols with an excess of polyisocyanates. Preferential blocking agentsare aliphatic alcohols, which can have a straight-chain, branched orring-like structure, such as, for example, methanol, ethanol, n-, iso-or tert.-butanol, hexanol, ethylhexanol, furfuryl alcohol, cyclohexanol,alkylglycols, alkyldiglycols and alkyltriglycols. Other known blockingagents, such as oximes, lactams, ketones or malonic esters can, however,also be used.

It is possible, without difficulty, to modify only a fraction of theMannich bases (a) or of the epoxide resins (b) with polyisocyanates,whether this is because epoxide compounds containing or not containingaliphatic hydroxyl groups are present alongside one another or whetherfurther, unmodified epoxide compounds are added after the reaction withpolyisocyanate has been carried out.

The proportions in the reaction with the partially blockedpolyisocyanates are preferably so chosen that there is 0.01 to 1.0,preferably 0.05 to 0.5, mole of urethane groups to one mole of basicnitrogen in the finished reaction product, counting both the urethanebond between the reaction product and polyisocyanate and the urethanebond between blocking agent and polyisocyanate. The whole structure ofthe reaction product makes it possible to ensure that, after it has beenprotonated with acids as a carrier resin, finely divided, nonionicplastics can be dispersed in it in such a way that stable aqueousdispersions are formed, at a pH value of over 7, from which the cathodicdeposition of the coatings can be carried out at these pH values ofbetween 7 and 9.

In its protonated form, the carrier resin can be diluted with water. Ifrequired, it is possible for additional solvents, which must, however,be selected in such a way that they do not either incipiently dissolveor incipiently swell the finely divided, nonionic plastic, also to bepresent, such as, for example, alcohols, such as isopropanol, propanolor butanol, glycols or glycol ethers, such as ethylene glycol, propyleneglycol, ethylene glycol monoethyl ether, ethylene glycol monopropylether or ethylene glycol monobutyl ether, or other solvents, such astetrahydrofuran, aliphatic and/or aromatic hydrocarbons, esters, ethersor ether-esters, in order to affect advantageously the dissolvingproperties and dispersing properties of the carrier resin.

It is an important characteristic of the invention that the aqueousdispersion contains nonionic plastics dispersed in it as the finelydivided plastics. The finely divided, nonionic plastics are described as"plastic powders" in the text which follows. In the form of powderlacquers, they have already gained acceptance in the field of lacqueringmetal objects. These plastic powders are solid and easy to grind fromroom temperature up to temperatures of 100° C. They are not reactive inthe sense of undergoing film formation to give high-molecular materialsat temperatures as low as room temperature on their own or together withother compatible resins, such as the cationic carrier resin. However,under the conventional stoving conditions, which are at about 160° C.,they melt and combine with the cationic carrier resin on the coatedsubstrate to form a compatible film.

Suitable finely divided, nonionic plastics within the scope of thisinvention are plastic powders belonging to the group comprising epoxideresins, polyester resins, acrylate resins, polyurethane resins,polyamide resins, polyethylene, polypropylene and celluloseacetobutyrates. These plastic powders are all known and most of them areavailable commercially. All the powders of this type can be employed inthe aqueous dispersion according to the invention, provided that theyare compatible with the carrier resin. Incompatibility can readily berecognized by the fact that the coating separates into two layers whenstoved. The plastic powder can be dispersed in this form in the aqueousdispersion. However, it is also possible to use a plastic powdercontaining fillers. In this case, the pigments and/or fillers havealready been incorporated into the plastic powder during the preparationof this powder. The aqueous dispersion itself can then be free frompigments.

The aqueous pigment according to the invention is not limited merely tocontaining a single nonionic synthetic resin. Mixtures of two or moredifferent plastic powders can also be present. In this case one or otherplastic powder can contain pigments and/or fillers, but the otherplastic powder can be free from these additives.

Apart from the pigments and fillers, the plastic powders employed canalso contain small quantities of hardening agents and other additiveswhich regulate the flow behaviour of the powder during stoving. Theaction of these additives incorporated into the plastic powder cannot beadversely affected by the aqueous dispersion.

As is customary in other coating agents, the aqueous dispersion cansimilarly contain auxiliaries which can be deposited by electrophoresis,such as, for example, pigments, fillers, hardening catalysts, agents forimproving flow, anti-foaming agents, agents for improving adhesion andothers.

The ratio between the carrier resin and the plastic powder is importantfor using the aqueous dispersion for the production of stoved coatingson the surface of electrically conducting substrates, connected as thecathode, by cathodic deposition from a coating bath in a cathodicelectrocoating lacquering process, and the average particle size of theplastic powder is also important for the quality of the coatingdeposited.

The best results are obtained in the cathodic deposition if there are0.1 to 100 parts by weight of plastic powder, preferably 0.5 to 10 partsby weight of plastic powder, to 1 part by weight of carrier resin,relative to the pigment-free and filler-free powder. Besides the carrierresin and the plastic powder, the aqueous dispersion also contains,additionally, 0 to 10 parts by weight of pigments and/or fillers,preferably 2 to 5 parts by weight.

The particle size of the plastic powder is an important factor. Theplastic powder should have a particle size distribution in which atleast 95% of the particles are smaller than 30 μm. The best results areobtained using plastic powders, which are therefore preferred, in whichat least 95% of the particles are smaller than 10 μm. It has been foundthat the particles of the plastic powder are more readily coated by thecarrier resin as their size decreases. For this reason the cathodicdeposition of finer particle sizes is easier and more even.

The aqueous dispersion is prepared by the methods which are knwon in thepaint industry. Thus the plastic powder can be stirred directly into theaqueous solution or dispersion of the protonated carrier resin by meansof a high-speed dispersing apparatus. Another possible means consists injointly incorporating the plastic powder, together with the desiredpigments and/or fillers, into the aqueous solution of the protonatedcarrier resin in a ball mill or a stirred ball mill.

A further possible means of preparing the aqueous dispersion consists inmixing an aqueous suspension of a plastic powder directly into theaqueous solution of the carrier resin. This method dispenses with theinvolved grinding process by means of a sand mill, a triple roll mill ora stirred ball mill.

In order to facilitate the preparation of the aqueous dispersion, it ispossible to effect the incorporation of the solid component in thepresence of small quantities of emulsifiers. Examples of suitableemulsifiers are nonionic emulsifiers of the type of ethylene oxideadducts of varying chain lengths, such as, for example, alkylphenolsmodified with ethylene oxide, for example tertiary octylphenol which hasbeen modified with 5 to 40 ethylene oxide units. Also higher aliphaticalcohols modified with ethylene oxide, such as, for example, laurylalcohols containing 15 to 50 ethylene oxide units, and also similarlymodified long-chain mercaptans, fatty acids or amines. Preferredmixtures consist of at least two ethylene oxide adducts in which theethylene oxide units have different values. The bath stability and theproperties of the coating are not substantially affected by theadditives.

Cationic emulsifiers, such as, for example, low-molecular aminocompounds which contain OH groups and which have been protonated withorganic or inorganic acids, are also suitable. The quantities ofemulsifiers should not exceed 0.1 part by weight, relative to thequantity of carrier resin.

The aqueous dispersion according to the invention is preferentiallysuitable for the cataphoretic deposition of a coating on an electricallyconducting substrate which is connected as the cathode in anelectrocoating lacquering process. For carrying out the cathodicdeposition, the aqueous dispersion is diluted with water down to asolids content between 5 and 30%, preferably between 5 and 15%. The pHvalue is between 7 and 9. During the cathodic deposition, the dispersionis kept at temperatures between 15° and 40° C. The substrate to becoated is immersed in the dispersion and is connected as the cathode.The anode used is graphite or a noble meal. A direct current is passedthrough the bath between the cathode and the anode. The depositionvoltage is 20 to 400 volts. Under these conditions a coating isdeposited on the cathode. Deposition is carried out until the desiredfilm thickness has been achieved. It is a particular advantage that filmthicknesses of up to 150 μm are obtained on the coated substrate evenafter a brief period. Depending on the plastic powder chosen, periods aslow as 10 seconds are adequate in some cases to obtain these filmthicknesses. After the substrate has been removed from the coating bath,the coating is rinsed with water and is stoved for 5 to 30 minutes attemperatures between 160° C. and 200° C. In some cases it is appropriateto interpose a brief preliminary drying at 100° C. before stoving.

It was surprising that the powder resin is deposited on the cathodetogether with the carrier resin. This would not have been expected,since dispersions composed of finely divided powder resin cannot bedeposited by electrophoresis.

Since the electrocoating bath becomes depleted in both the carrier resinand the plastic powder during the deposition process, it is necessary toreplenish the bath with these substances, so that the originalcomposition of the aqueous dispersion is always maintained. The pH valuemust be kept at 7 to 9 during the whole deposition process.

The properties of the stoved coating are excellent from a technologicalpoint of view. The corrosion resistance is surprisingly good and varieswith the nature of the solid powder lacquers. Using the aqueousdispersion according to the invention, a very high film thickness isachieved, which, of course, somewhat impairs the throwing power. Thestoved film can be subjected without difficulty to further lacqueringusing conventional lacquers. The examples which follow are intended toillustrate the essence of the invention, but not to limit it.Percentages relate to percentages by weight; parts relate to parts byweight.

EXAMPLE 1 (Preparation of a Carrier Resin)

984 parts (13.1 moles) of 40% strength formaldehyde solution are addeddropwise at 20° to 25° C. to 1,100 parts (4.8 moles) of bisphenol A,917.5 parts (8.7 moles) of diethanolamine, 332.5 parts (2.5 moles) ofdi-2-methoxyethylamine and 375 parts of isopropanol. The mixture isstirred for one hour under a nitrogen atmosphere at 30° C. and is thenheated at 80° C. for 3 hours. Isopropanol and water are removed bydistillation under a slight vacuum. This gives a yellow, resin-like masswith a solids content of 91%. 70 parts of paraformaldehyde are added to2,542 parts of the above and the mixture is subjected to a condensationreaction for 9 to 10 hours at 70° C. under a nitrogen atmosphere. AMannich base (component A) is obtained in the form of a viscous masshaving a solids content of 90%.

544 parts of this Mannich base are reacted for 3 hours at 60° C. with136.5 parts of a commercially available reaction product formed frombisphenol A and epichlorohydrin (epoxide value: 0.2) (epoxide resinEpoxy 1/33 manufactured by Chemapol) and 54.5 parts of a commerciallyavailable reaction product formed from pentaerythritol andepichlorohydrin (epoxide value: 0.57) (Epoxin 162, BASF AG), using 34parts of dimethyl glycol ether.

This gives a clear, viscous resin having an average molecular weight of860 and a residual formaldehyde content of 0.3%. The solids content is70%.

EXAMPLE 2 (Preparation of a Nonionic Plastic Powder)

100 parts of an epoxide resin powder formed from bisphenol A andepichlorohydrin, having a Kofler melting range of 70° to 75° C., 3 partsof a levelling agent, 20 parts of titanium dioxide (rutile grade), 8parts of aluminum silicate, 2 parts of red iron oxide and 5 parts of adicyandiamide derivative are melted and kneaded together in an extruderin the manner customary for the preparation of pulverulent coatingagents. After solidifying the mixture is ground in a spiral jet mill togive a powder with a maximum particle size of 30 μm and an averageparticle size of 10 to 15 μm.

EXAMPLE 3 (Preparation of a Nonionic Plastic Powder)

A. 60 parts of a pulverulent polyester resin and 50 parts of an epoxideresin formed from bisphenol A and epichlorohydrin, having a Koflermelting range of 70°-75° C., are dissolved in 290 parts of diacetonealcohol. This solution is stirred into water by means of a high-speeddisperser and the resin mixture is precipitated. The precipitate isfiltered off.

B. The moist filter cake is washed with water and dried in a drying ovento give a solid powder, which is then ground in a spiral jet mill to amaximum particle size of 30 μm. 95% of the powder has an averageparticle size distribution between 10 and 15 μm.

C. The moist precipitate obtained in accordance with A. is washed withwater and filtered off again. The filter cake is suspended to form ahomogeneous composition with enough water for this composition tocontain one part of synthetic resin powder and two parts of water. Theaverage particle size distribution of the powder is 5 to 10 μm; themaximum particle size is 30 μm.

EXAMPLE 4

100 parts of the carrier resin prepared in accordance with Example 1 areprotonated with two parts of acetic acid and dispersed in 800 parts ofcompletely demineralized water. 100 parts of the plastic powder obtainedin accordance with Example 3B are added to this dispersion of clearlacquer while stirring well.

The solids content of the dispersion is adjusted to 12%; its pH value is7.6. Its conductivity is 0.7 millisiemens/cm at 25° C.

A phosphatized sheet of steel is immersed in this dispersion andconnected as the cathode. A sheet of stainless steel is immersed andconnected as the anode.

Applying a direct current at a voltage of 250 volts and a bathtemperature of 24° C., a coating was deposited on the cathode sheet for20 seconds. The sheet which has been provided with the coating is takenout and rinsed with completely demineralized water and is then stovedfor 20 minutes at 185° C. A continuous film having a film thickness of40 to 50 μm is formed on the side of the sheet facing the anode. In thecorrosion resistance test as specified in DIN 50,021, the film was stillin a satisfactory condition after 1,000 hours.

EXAMPLE 5

100 parts of the carrier resin prepared in accordance with Example 1 areprotonated with two parts of acetic acid and dispersed in 800 parts ofcompletely demineralized water. 200 parts of the plastic powder obtainedin accordance with Example 2 are added to this dispersion of clearlacquer, while stirring well.

The solids content of the dispersion is adjusted to 12% and its pH valueis 7.6. Its conductivity is 0.7 millisiemens/cm at 25° C.

A phosphatized sheet of steel is immersed in this dispersion andconnected as the cathode. A sheet of stainless steel is immersed andconnected as the anode. A coating was deposited on the cathode sheet for30 seconds, applying a direct current at a voltage of 200 volts and abath temperature of 24° C. The sheet which had been provided with thecoating was taken out and rinsed with completely demineralized water andwas then stoved for 20 minutes at 185° C. A continuous film with a filmthickness of 80 μm is formed on the side of the sheet facing the anode.In the corrosion test as specified in DIN 50,021, the film was still ina satisfactory condition after 1,000 hours.

EXAMPLE 6

100 parts of the carrier resin obtained in accordance with Example 1 areground for 72 hours in a ball mill with porcelain balls together with 10parts of titanium dioxide (rutile grade), 8 parts of aluminum silicate,2 parts of red iron oxide, 1 part of acetic acid, 600 parts of theplastic powder suspension obtained in accordance with Example 3C and 10parts of butanol. The solids content is then adjusted to 12% with waterand the resulting aqueous dispersion is deposited cathodicallyanalogously to Example 4. The deposition voltage was 150 volts; thedeposition time was 40 seconds. A film thickness of 80 μm was achieved,after stoving, on the side of the sheet facing the anode. The stovedfilm was polished and an alkyd resin/melamine resin stoving top lacquerwas applied by the spraying process and stoved for 20 minutes at 140° C.The Erichsen deep-drawing value of the whole lacquering was 10.3 mm, thecross-hatch immersion test rating was 0 and the resistance to salt sprayas specified in DIN 50,021 was 0 mm, after 720 hours.

EXAMPLE 7

Example 5 was repeated, except that two parts of anoctylnonylphenoxyethanol emulsifier (Triton 405 manufactured by Rohm &Haas Company, Philadelphia, U.S.A.) was also added, in addition to thecarrier resin.

The plastic powder was then stirred into the mixture containing theemulsifier. The results obtained were similar to those of Example 5.

EXAMPLE 8

A steel sheet is immersed half way in the dispersion prepared inaccordance with Example 5, having a solids content of 12% and a pH valueof 7.6, and is earthed via a contact. The dispersion is stirred atuniform speed and, after 20 days, no corrosion or rust phenomena can bedetected on the steel sheet, specifically neither on the immersed partnor on the part not immersed.

In a comparison experiment, Example 1 of German Auslegeschrift No.2,248,836 was repeated and, in accordance with this example, thedispersion was diluted to a solids content of 12% and adjusted to a pHvalue of 4.4 to 4.5. A steel sheet was also immersed in this dispersionand the dispersion was stirred continuously. After 5 days, corrosionphenomena made themselves evident on the steel sheet, specifically aspitting on the part immersed in the liquid and as rust formation on thepart located above the coating bath.

This experiment demonstrates the superiority of the dispersion accordingto the invention over a dispersion according to the known state of theart.

We claim:
 1. In an aqueous dispersion consisting of an aqueous solutionand/or aqueous dispersion of a reaction product, protonated with acids,from the reaction of (a) Mannich bases which are free from epoxidegroups with (b) epoxide resins wherein aliphatic hydroxyl groupsoriginating from (a), (b) or a mixture thereof are at least partiallyconverted into urethane groups by reaction with partially blockedisocyanate, said Mannich bases (a) formed from components selectedfrom:(a₁) condensed phenols which are free from ether groups and containat least two aromatic rings and at least two phenolic hydroxyl groups;(a₂) condensed phenols which contain ether groups and contain at leasttwo aromatic rings and at least two phenolic hydroxyl groups; (a₅)formaldehyde or compounds which split off formaldehyde; and (a₃)secondary amines having at least one hydroxyalkyl group or a mixture ofa₃ and (a₄) secondary dialkylamines or dialkoxyalkylamines which do notcontain free hydroxyl groups or from the components (a₁) or (a₂) with(a₅) and (a₃) or a mixture of (a₃) and (a₄), the improvement whichcomprises said dispersion having a pH between 7 and 9 and havingdispersed therein finely divided, non ionic plastics selected from thegroup consisting of epoxide resins, polyester resins, acrylate resins,polyurethane resins, polyamide resins, polyethylene, prolypropylene,cellulose acetobutyrates and mixtures thereof.
 2. Aqueous dispersions asclaimed in claim 1, wherein the aqueous solution and/or aqueousdispersions of the reaction product which has been protonated with acidscontains pigments, fillers, water-miscible organic solvents or mixturesthereof.
 3. An aqueous dispersion as claimed in claim 1 wherein thefinely divided plastics contain pigments, fillers or mixtures thereof.4. An aqueous dispersion as defined in claim 1 wherein said nonionicplastics comprise 0.1 to 100 parts by weight of plastic powder to 1 partby weight of said carrier resin product.
 5. An aqueous dispersion asdefined in claim 4 wherein said plastic powder has a particle sizedistribution in which at least 95% of the particles are smaller than 30microns.
 6. An aqueous dispersion as defined in claim 5 wherein saidnonionic plastics comprise 0.5 to 10 parts by weight of plastic powderto 1 part by weight of said carrier resin product.
 7. An aqueousdispersion as defined in claim 6 wherein said plastic powder has aparticle size distribution in which at least 95% of the particles aresmaller than 10 microns.
 8. An aqueous dispersion as defined in claim 1,wherein said nonionic plastics are epoxide resins.
 9. An aqueousdispersion as defined in claim 1, wherein said nonionic plastics arepolyester resins.
 10. An aqueous dispersion as defined in claim 1,wherein said nonionic plastics are polyurethane resins.
 11. An aqueousdispersion as defined in claim 1, wherein said nonionic plastics arepolyamide resins.
 12. An aqueous dispersion as defined in claim 1,wherein said nonionic plastics are polyethylene.
 13. An aqueousdispersion as defined in claim 1, wherein said nonionic plastics arepolypropylene.
 14. An aqueous dispersion as defined in claim 1, whereinsaid nonionic plastics are cellulose acetobutyrates.